Current high-performance golf club heads are often manufactured from substantially unitary metal or graphite structures. In attempts to maintain low weight, while having large volumes, in the case of drivers (commonly referred to as “woods”), the heads are often made of materials such titanium, steel or graphite composites.
Many performance characteristics are desirable in the case of driver heads, including size, strength, mass distribution/inertia properties and sound. For example, generally, as the size of the heads increases (many approaching 500 cc), the heads tend to be more “forgiving” for off-center hits.
Higher strength heads, particularly with respect to the face of the head, are likewise desirable as reduction of the combined deflection of the face and ball upon impact preserves energy from club to ball. Stated otherwise, using stronger, yet thinner materials in the face provides the ability to decrease the deflection in the ball (where the most energy loss occurs) by increasing the deflection in the face. To that end, faces have been manufactured from stronger materials than the remainder of the head. For example, some heads have faces manufactured of materials such as Beta titanium, which are welded to head bodies made of weaker materials such as cast titanium.
Further still, more and more, golfers seek club heads with specific centers of gravity locations and moments of inertia to control drive characteristics. Further yet, golfers increasingly seek to change certain subjective characteristics such as the sound made upon impact between the club head and the ball. For example, some golfers prefer the hollow “ping” sound of a titanium driver, while others prefer the “dead” or solid sound of a composite head (more like a traditional wood driver).
These various performance attributes combine to allow club designers to tune or enhance certain characteristics of club performance. However, conventional metal design/construction methods are limited by basic properties (e.g., stiffness, strength and density) of the metal as well as by manufacturing limitations (e.g., casting, welding and forming). Similarly, composite heads have limitations including durability “out of plane” or perpendicular to the fiber plane. For example, loads at impact tend to de-laminate the composite layers and yet, when a design is created with sufficient strength to survive the impact loads, the resulting face is very thick which increases stiffness causing more deflection in the ball reducing the conversion of energy to the ball at impact.
Thus, while the above-mentioned attributes are sought, many remain unrealized. Improved heads which can vary stiffness and strength areas redistribute total weight allowing control of the location of center of gravity and moment of inertia and/or are made of lighter and stronger materials, allowing bigger club heads with correspondingly larger “sweet” spots. Further still, clubs which provide “tunable” centers of gravity and moments of inertia are also desirable. Such clubs may be further capable of producing varying impact sounds, and are therefore desirable.